In the above-cited patent application there is disclosed a wall duct assembly comprising a duct having on its outer surface retaining grooves in which are provided seals. These seals can be axially compressed so that when the unit is cast into a wall axial compression of the seals forces them radially outwardly against the wall, radially inwardly against the tube, and axially in one direction also against the wall, thereby forming an excellent seal.
Such an arrangement has, however, the disadvantage that two seals must be used, so that the construction costs are somewhat elevated. Furthermore the device is frequently fouled when the cable, pipe, or the like is passed through the duct, as the inner surface of the seal is exposed when the cover or end piece for the unit has been removed.